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Connectors Enable Precise Movement of Lunar Robotic Tool Changer

Saturday, 01 December 2012

Page 1 of 2

NASA’s Langley Research Center in
Hampton, VA hired Honeybee
Robotics Spacecraft Mechanisms Corp.
to develop a totally mechanical tool
changer for the end of what Langley’s
Lunar Surface Manipulation System
(LSMS) team describes as a robot that
could unload landers. Then, after the
landers were unloaded, it could, in addition
to doing base assembly, mate with
tools to take science experiments. This
robot could be likened to a crane, but
with more dexterity.

The crane was designed to work
remotely so that it could be used on an
unmanned mission without human
interaction. It is completely autonomous
— one of the driving factors. The tool
changer does have other applications if
they decide they want to use it on Mars
or even in outer space for a robotic arm
and end effectors.

Since Honeybee has been developing
harsh-environment, mission-critical end
effectors for over 25 years and has
worked on the equipment for other
space missions, they were specially suited
to tackle this challenge.

Making It Work

Basically, Honeybee was given a footprint
to stay within, and all the requirements
for load ratings and misalignment
allowances. Explained Lee Carlson, a systems
engineer who was part of the
Honeybee team, “The crane might be
sitting on the lander deck or on the
lunar surface and would be driven from
quite a distance away from the tool to be
mated to. This required designing for
large misalignment allowances. This was
our first design challenge. The end of
the crane and target tool could be misaligned
by as much as a couple inches in
any direction with up to 20 degrees
angular misalignment when attempting
a mate.”

But, Carlson continued, there were
other considerations. “The tool changer
had to be capable of carrying around
1,000 pounds, so (the tool changer) had
to be very robust. Also, since this was a
lunar project, it has to be tolerant to
moon dust. These two design criteria
required special seals to protect large
roller bearings. If this design was for
space, it becomes considerably simpler.
All of the loads would be reduced and
dust is no longer an issue. But the Moon
is a very harsh environment, and lunar
dust is a major concern when designing
for missions there.”

The original assignment called for
‘dummy’ tools requiring no power; the
crane would do all the work. Tools
would range from a forklift attachment,
a shovel, or scoop for acquiring surface
samples or digging, to a bucket for lifting
human passengers.

Then NASA decided it wanted the
capability of attaching an electronic or
electromechanical tool to the end of the
crane. Now, the tool changer would have
to provide an electrical connection as
well. Solving this problem fell to
Carlson. “The contract was expanded to
add an electrical connector to the existing
mechanical connector. You’d have a
power source on the LSMS, on the crane
itself. Your tools could then be powered.
So your tools capabilities could expand
into the realm of cameras, or tools with
cameras on them, or even a light jackhammer.”
However, they had not left
space to accommodate an electrical connector
because it was not a part of the
original contract and the budget did not
allow for starting from scratch.

A Crucial Ten Square Inches

Carlson had to work within the constraints
of the current design because
NASA did not want a redesign of the
whole tool changer. They just wanted to
add an electrical connector to it without
increasing the current envelope. He
only had roughly 2-1/2 by 4" of free
space to incorporate the male side of the
new autonomous connector. The connector
has to mate itself to a female connector
mounted on the tool. Carlson
said, “We make small stuff all the time
and if there were more space, there are
many different ways that I could have
designed it.”

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